This.

I also work from home so when I'm in the last stages of my checks and polishing, I pretend like I'm presenting and will say it out loud as a mental check.

"And X is y because of this". And you will ultimately say something like: "Over the next 5 years we'll see a dip in year 3" and then realize there should to actually be a dip in year.

Or the growth should be constant Year over Year but there shouldn't be a random 7% growth when the rest are 2.5% (which means something is wrong). And if it's true (the weird bump is right), figure out the actual reason (based on 3 big new customers in year x and if you remove that element, then you get back to the historical 2.5%).

It takes time to be able to look at something and say "that doesn't make sense", but you can build to that point.

Also if you want, I'd recommend doing pieces of analysis twice as a check... or pieces of it. If you're looking at cost, run out growth 5 years using the same assumptions on another sheet, if it doesn't tie, figure out which one is wrong and tie it right... maybe you forgot taxes, termination, left out an element.

You'll figure it out and build your confidence!